Method of making water-blown polyurethane sealing devices

ABSTRACT

A particular isocyanate prepolymer composition particularly suitable for use in polyurethane compositions having particular applicability for producing microcellular molded polyurethane articles and is particularly suitable for use in sealing devices. In particular, the isocyanate prepolymer composition is the result of reacting an isocyanate blend (a) having 
     (i) 0 to 10 pbw 2,4&#39;-diphenylmethane diisocyanate; 
     (ii) 30 to 80 pbw 4,4&#39;-diphenylmethane diisocyanate; 
     (iii) 1 to 10 pbw of a mixture of uretonimine 
     with from 10 to 70 parts by weight of a polyol (b) having a number average molecular weight of between 1000 and 10,000, and a hydroxyl number of between 10 to 75. The resulting isocyanate prepolymer (I) has a free NCO of less than 20 and a viscosity of from 200 to 1000 cPs.

This is a division of application Ser. No. 08/367,036 filed Dec. 29,1994, now abandoned.

BACKGROUND OF THE INVENTION

The invention provides water-blown polyurethane sealing devices andcompositions for producing such devices. More particularly, theinvention provides isocyanate prepolymer compositions and polyurethanecompositions containing such prepolymer compositions, both compositionsbeing especially suitable for the preparation of polyurethane sealingdevices having advantageous performance properties such as improvedhardness and compression characteristics.

Various aspects of the polyurethane industry have seen increasinggovernment regulation in the area of acceptable blowing agents. This hasbeen especially true for those involved in the production ofpolyurethane foams and molded microcellular polyurethane articles. Inparticular, due to environmental concerns relating to the earth'satmosphere and ozone levels, it is now highly desirable to replacecertain physical blowing agents with alternative blowing agents.

Although research continues in the development of new blowing agents,renewed attention has been directed toward the use of water as aprincipal blowing agent. Desirable because of its low cost, readyavailability, and minimal safety hazards, the use of water as a blowingagent nonetheless presents several problems.

Polyurethane polymers of the sort to which the instant invention isdirected may generally be identified as having primary chainscharacterized by a segmented or block co-polymer structure. The segmentsare generally identified as being either "hard" or "soft" segments. Softsegments are the residual of long chain polyether or polyester polyolsand are generally more flexible. Hard segments are formed from theresidual of the diisocyanate and a short chain diol or chain extender.

The use of water as the principal blowing agent in the production ofmolded, microcellular polyurethane foams results in the incorporation ofshort brittle segments in the polymer matrix. These brittle segments areless forgiving to stress and detract from the overall physicalproperties of the resulting polymer. Properties such as flexibility,abrasion resistance, hardness, strength, and fatigue resistance appearto be particularly vulnerable. In addition, principally water blownpolyurethane compositions appear to be somewhat inferior with respect totheir ability to perform in a variety of processing latitudes, i.e.exhibit adequate flowability and/or demold times in molding operations.

As a result of these problems, certain segments of the polyurethaneindustry have found it difficult to adapt their formulations to 100% orprincipally water blown. The switch to water blown polyurethaneformulations has been most difficult where the resulting microcellularpolyurethane article must meet vigorous performance requirements.

An illustrative example is the production of sealing devices. The term"sealing device" is intended to encompass devices such as gaskets, airfilter seals and end caps, as well as covered gaskets for the same.Common applications for such sealing devices include use on all types ofmotor driven vehicles, including, but not limited to, gas and dieselpowered cars, trucks, and heavy equipment.

The operating environments of these devices often require that theyfunction in extremes of temperature and pressure. Depending upon theend-use application, such sealing devices are often subjected tocorrosive and/or structurally altering materials such as oil andgasoline. Performance properties evidencing strength, hardness, andcompression characteristics have been found to be of paramountimportance in the design and production of sealing devices. Inparticular, the characteristics measured by compression forcedeflection, tensile strength, and compression set have been found to beparticularly vital. In general, measures taken to improve one of theseproperties often have detrimental effects on one or both of the otherproperties. An optimum balance between the three properties has beendifficult to achieve in sealing devices.

As a result, it has been particularly difficult to provide water blownpolyurethane compositions capable of providing molded microcellularpolyurethane foams having the performance and processing propertiesrequired of commercially acceptable sealing devices.

The prior art has unsuccessfully attempted to address these problems.Several attempts have focused on the use of particular isocyanateprepolymers.

For example, U.S. Pat. No. 4,287,307 to Hostettler, disclosesisocyanate-terminated prepolymers which are obtained by the reaction of(i) symmetrical aliphatic diisocyanates, cycloaliphatic diisocyanates,aromatic diisocyanates, or mixtures of such with their carbodiimidederivatives, with (ii) hydroxyl-terminated mono- or polyesters, orcertain glycols or polyoxyalkylene glycols. However, the properties ofthe resulting foams are such that one or more plasticizers having one offour delineated structures must be used to obtain foams which are usefulas shoe soles, vibration dampening devices, floatation devices, gasketsand the like. Also, example 4 of the '307 patent teaches thatundesirable performance characteristics are obtained with water blownfoams.

U.S. Pat. No. 4,321,333 to Alberino et al, discloses the use of aorganic polyisocyanate (A) in the production of polyurethane polymers.Polyisocyanate (A) is disclosed as a blend of a prepolymer (a) and aliquified methylene bis(phenylisocyanate) (b). The prepolymer (a) is areaction product of methylene bis(phenylisocyanate) with a polyolmixture comprising (1) a polyol having a molecular weight of at least1,000, and (2) a polyol having a molecular weight of about 115 to 300.The '333 patent teaches that the additive prepolymer (a) in theisocyanate blend acts as an annealer to allow the curing of moldedpolyurethanes at temperatures lower than those prior art moldedpolyurethanes while resulting in improved green strength. However, theresultant foams do not appear to have the physical properties requiredof commercially acceptable sealing devices. In particular, the '333patent fails to disclose important performance properties such ascompressive force deflection and compression set.

In U.S. Pat. No. 4,374,210 to Ewen et al, the preparation ofpolyurethane-polyureas using aromatic diamine extenders is disclosedwherein certain prepolymers of 4,4'-methylene bis(phenylisocyanate) areused in place of 4,4'-methylene bis(phenylisocyanate) itself. Theparticular prepolymers are derived from the reaction of 4,4'-methylenebis(phenylisocyanate) with polyoxyethylene polyoxypropylene polyetherdiols and triols having molecular weights from 1,000 to 10,000,polytetramethylene glycols having molecular weights from 600 to 5,000,and polyester diols and triols having molecular weights from 500 to8,000. However, this invention is directed toward the production ofpolyurea-urethanes requiring the use of aromatic diamines. The resultantmoldings do not have the performance properties required of sealingdevices.

U.S. Pat. No. 4,559,366 to Hostettler, relates to improved integral skinmicrocellular polyurethane elastomers intended for use as shoe soles.The disclosed improvement relates to the use of quasi-prepolymers whichare normally liquid, may have crystalline points as low as -20° C., andare derived from the reaction of (1) a mixture of normally soliddiphenylmethane diisocyanate, carbodiimide and/or uretoneimine and (2)poly(oxyethyleneoxypropylene) polyols. However, the disclosures of the'366 patent are particularly directed toward the production of integralskin microcellular polyether polyurethane elastomer products havingspecific gravities in the range of about 0.4 to 0.7 gm/cm³. In addition,the patent expressly teaches that the elimination of water as asecondary blowing agent is preferred, and that blowing is mostpreferably effected with halocarbons.

Finally, published PCT application WO 92/22595 by the Dow ChemicalCompany, discloses a process for preparing polyurethane elastomer from asoft-segment isocyanate-terminated prepolymer. The prepolymer isobtained by reacting a molar excess of polyisocyanate having at least 70weight percent 4,4'-methylene diphenylisocyanate, with anisocyanate-reactive composition containing (a) a branched diol or triolhaving a molecular weight of from 60 to 300, and (b) a polyoxyalkylenepolyol or mixtures thereof having an average functionality of from 2 to4 and a molecular weight of from 3000 to 12000, wherein the parts byweight ratio of (a):(b) is from 0.01:1 to 0.25:1. However, therequirement of the particular branched diols or triols adds to the costof the composition. The resultant foams fail to provide the performanceproperties required of sealing devices due to the brittlenessincorporated by the short claim diols in the polymer backbone.

Thus, it would be highly desirable to provide a principally water blownpolyurethane composition capable of providing molded microcellularpolyurethane articles having advantageous performance properties such asimproved hardness, strength, and compression which are especially suitedfor use as sealing devices.

Accordingly, it is an object of this invention to provide principallywater blown polyurethane compositions which are particularly suitablefor the preparation of molded microcellular polyurethane articles havingadvantageous performance properties such as improved hardness,strengths, and compression characteristics.

More particularly, it is an object of this invention to provideprincipally water blown polyurethane compositions which are particularlysuited for the preparation of molded microcellular polyurethane sealingdevices exhibiting an optimum balance between the values for compressionforce deflection, tensile strength, and compression set.

It is a further object of this invention to provide isocyanateprepolymer compositions particularly suitable for use in polyurethanecompositions which are solely or principally water blown and which areused in the production of molded microcellular polyurethane articles.

It is an additional object of the invention to provide isocyanateprepolymer compositions intended for use in principally water blownpolyurethane compositions used in the production of microcellular moldedpolyurethane articles exhibiting desirable values for compression forcedeflection, tensile strength, and compression set.

Finally, it is an object of this invention to provide moldedpolyurethane articles and a process for making such, wherein theresulting molded polyurethane articles have an optimum balance betweenhardness, Strength, and compression characteristics, such as desirablecompression set, tensile strength and compression force deflectionvalues.

SUMMARY OF THE INVENTION

The foregoing objects, as well as others, are achieved by the followingaspects of the invention.

The invention provides an isocyanate prepolymer composition (I) which isa result of reacting the isocyanate blend (a) having

(i) 0 to 10 pbw 2,4'-diphenylmethane diisocyanate;

(ii) 30 to 80 pbw 4,4'-diphenylmethane diisocyanate; and

(iii) 1 to 10 pbw of a mixture of uretonimine containing molecules andcarbodiimide containing molecules; and

(b) from 10 to 70 pbw of an ethoxylated and propoxylated glycerinehaving a number average molecular weight of between 1000 and 10,000 anda hydroxyl number of between 20 to 100;

wherein the resulting prepolymer has a % free NCO of less than 20% and aviscosity of from 200 to 600 cPs and all pbw are based on the totalweight of (a) and (b).

The invention further provides a polyurethane composition suitable forthe preparation of molded polyurethane articles, the compositionrequiring the above isocyanate prepolymer composition (I), an isocyanatereactive component (II), a chain-extender (III), and a blowing agentwhich is principally water.

Finally, the invention provides a process of molding polyurethanearticles, as well as the articles produced therefrom. The processrequires providing a polyurethane composition as described immediatelyabove.

The described polyurethane composition is placed inside a mold for aperiod of time sufficient to produce a molded polyurethane article. Theclaimed molded polyurethane articles have an optimum balance ofdesirable compression characteristics, hardness and strength properties.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While not wishing to be bound to a particular theory, it is believedthat the ability of the invention to provide solely or principally waterblown polyurethane compositions capable of providing moldedmicrocellular polyurethane articles which evidence an optimum balance ofproperties, results from the use of the particular isocyanate prepolymercomposition (I) of the invention.

The isocyanate prepolymer compositions (I) of the invention consistsessentially of the reaction product obtained by the reaction of anisocyanate blend (A) and a particular polyol (B).

Isocyanate blend (a) is a particular mixture of a isocyanate-containingspecies. While not wishing to be bound to a particular theory, theranges set forth below are believed to be necessary to obtain thedesired performance properties described herein.

Isocyanate blend (a) has been found to be useful in achieving theobjectives set forth above, when the blend contains particular amountsof certain diisocyanate monomers and uretonimine containing moleculesand carbodimide containing molecules. In particular, it has been foundthat isocyanate blend (a) should contain (i) 2,4'-diphenylmethanediisocyanate, (ii) 4,4'-diphenylmethane diisocyanate, and (iii)uretonimine-carbodimide derivatives of diphenylmethane diisocyanate.

The (i) 2,4'-diphenylmethane diisocyanate and (ii) 4,4'-diphenylmethanediisocyanate species may be provided by commonly availablediphenylmethane diisocyanates (MDI). Suitable MDI's may be either pure,i.e. solely 4,4'-MDI or mixtures containing both 4,4'-MDI and 2,4'-MDIisomers. If mixtures of MDI isomers are utilized, it is preferred thatthey contain less than 2 percent by weight of 2,4'-MDI isomers.

In addition, isocyanate blend (a) will further containuretonimine-carbodiimide derivatives of essentially pure diphenylmethanediisocyanate. Such mixtures of uretonimine-containing molecules andcarbodiimide-containing molecules can be made by well-known techniques,such as the conversion of a portion of the isocyanate groups indiphenylmethane diisocyanate to a carbodiimide by usingphosphorus-containing catalysts at elevated temperatures, then allowingthe carbodimide modified diphenylmethane diisocyanate to further reactwith unreacted isocyanate groups to form uretonimine modified MDI. Thoseskilled in the art will appreciate that the conversion from carbodiimidemodified uretonimine modified MDI does not typically go to completion,resulting in a composition containing both carbodiimide containingmolecules and uretonimine containing molecules. Typically from about 10to 35 percent by weight of the MDI is converted to uretoniminecarbodiimide modified MDI species, leaving generally from 65 to 95percent of the MDI unreacted.

As indicated from the foregoing discussion, it can be seen thatisocyanate blend (a) can be generally comprised of a mixture of variouscommercially available isocyanates. However, it has been found that inorder to obtain the desired end use advantageous performance properties,the prepolymers of the instant invention require that the abovemolecular species be present in particular amounts as based on the totalamount of isocyanate blend (a) and a particular polyol (b).

It has been found that isocyanate blend (a) should have from 0 to 10parts by weight 2,4'-diphenylmethane diisocyanate, 30 to 80 parts byweight 4,4'-diphenylmethane diisocyanate and 1 to 10 parts by weight ofa mixture of uretonimine containing molecules and carbodiimidecontaining molecules.

More particularly, it had been found that based on the weight of both(a) and (b), isocyanate blend (a) should have from 0 to 5 parts byweight 2,4'-MDI, 40 to 70 parts by weight 4,4'-MDI, and 1 to 7 parts byweight of a mixture of carbodiimide containing molecules and uretoniminecontaining molecules.

Finally, it is most preferred that isocyanate blend (a) have from 0 to 3parts by weight 2,4'-MDI, 45 to 65 parts by weight 4,4'-MDI, and from 1to 5 parts by weight of a mixture of carbodiimide containing moleculesand uretonimine as based on the total amount of (a) and (b).

It will be appreciated by those skilled in the art that the amounts ofcommercially available isocyanates to be used in making isocyanate blend(a), will depend on the respective percentages of the particularisocyanates species contained therein. The working examples set forthbelow indicate the particular amounts of illustrative commerciallyavailable isocyanates to be used in obtaining isocyanate blend (a).

Isocyanate blend (a) will be blended with a particular polyol (b) whichwill be an ethyoxylated/propoxylated triol. In particular, the polyol(b) will be an ethyoxylated/propoxylated glycerine or trimethanolpropane (TMP). The most preferred initiator is TMP. With respect to thealkylation of the triol, in general there will be a minimum of a 3:1ratio with respect to the amount of propoxylation and ethyoxylation.More particularly, the polyol (b) will have a least 75 percent of POwith the remainder being EO. It is preferred that the residual ethyleneoxide linkages be present as a cap.

Suitable polyol (b) will generally have a number average molecularweight of between 1,000 to 10,000. A preferred polyol (b) will have anumber average molecular weight of from 2,000 to 7,000, while the mostpreferred polyol (b) will have a number average molecular weight ofbetween 4,000 to 6,000.

In addition, the polyol (b) may be characterized by its hydroxyl number.Suitable polyols will have a hydroxyl number of between 10 to 75.Preferred polyols (b) will have a hydroxyl number of between 15 to 50,while the most preferred polyol (b) will have a hydroxyl number ofbetween 20 to 30.

Finally, the particular polyol (b) will be reacted with isocyanate blend(a) in an amount of between 10 to 70 parts by weight based on the totalamount of isocyanate blend (a) and polyol (b). More preferably, polyol(b) will be present in an amount of from between 20 to 60 parts byweight, while most preferably, isocyanate blend (a) will be reacted withof between 30 to 50 parts by weight polyol (b) as based on the totalamount of (a) and (b).

The method of making the isocyanate prepolymer composition (I) requiresthat isocyanate blend (a) be reacted with polyol (b) to form aprepolymer composition. In general, the ingredients of isocyanate blend(a) will preferably be charged to a reactor which is heated to atemperature sufficient to make any solid MDI based components molten orliquid. Subsequently, a sufficient amount of a polyol (b) will be addedto the heated reactor.

The reactor contents will subsequently be heated to a temperature ofbetween 25° C. and 100° C. More preferably, the reaction betweenisocyanate blend (a) and polyol (b) will take place at temperaturesbetween 50° C. to 80° C.

The reaction between reactants (a) and (b) will preferably take placefor a time sufficient for the final isocyanate prepolymer composition(I) to have a free NCO content of less than 20 percent. In general, thereaction polyol (b) with isocyanate blend (a) will take a maximum of tenhours and preferably less than a total of seven hours. Most preferred isa reaction time of five hours or less. At the conclusion of the reactionprocess the isocyanate prepolymer composition (I) of the inventionshould have a free NCO content of less than 20 percent by weight. Morepreferably, the claimed isocyanate prepolymer composition (I) will havea free NCO content of from about 15 to 20 percent by weight while themost preferred isocyanate composition (I) will have a percent NCO offrom about 17 to 19 percent by weight.

The viscosity of the resulting isocyanate prepolymer composition willgenerally be from about 200 to 1,000 cPs at 25° C. The preferred rangewill be from about 200 to 800 cPs while the most preferred viscositieswill be from 300 to 600 cPs (all at 25° C.).

In general, the prepolymer composition (I) will be added to a resin sidecomponent comprised of an isocyanate-reactive component (II), achain-extender (III), a blowing agent (IV), and optionally one or moreadditives (V) selected from the group consisting of surfactants,catalysts, stabilizers, dyes, fillers, pigments, flame inhibitors, andantioxidants, and mixtures thereof.

The isocyanate-reactive component (II) (also termed `polyol (II)`) maybe selected from compounds having at least two isocyanate reactivehydrogens which are commonly employed in the preparation of polyurethanefoams and elastomers. Such compounds are often prepared by the catalyticcondensation of alkylene oxide or a mixture of alkylene oxides eithersimultaneously or sequentially with an organic compound having at leasttwo active hydrogen atoms, such as evidenced by U.S. Pat. Nos.1,922,459; 3,190,927; and 3,346,557.

Representative isocyanate-reactive components, i.e. polyols, includepolyhydroxyl-containing polyesters, polyoxyalkylene polyether polyols,polyhydroxy-terminated polyurethane polymers, polyhydroxyl-containingphosphorous compounds, and alkylene oxide adducts of polyhydricpolythioesters, polyacetals, aliphatic polyols and thiols, ammonia, andamines including aromatic, aliphatic, and heterocyclic amines, as wellas mixtures thereof. Alkylene oxide adducts of compounds which containtwo or more different groups within the above-defined classes may alsobe used, for example, amino alcohols which contain amino groups and ahydroxyl group. Also, alkylene oxide adducts of compounds which containone SH group and one OH group as well as those which contain an aminogroups and an SH group may be used.

Any suitable hydroxy-terminated polyester may be used such as areprepared, for example, from polycarboxylic acids and polyhydricalcohols. Any suitable polycarboxylic acid may be used such as oxalicacid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelicacid, suberic acid, azelaic acid, sebacic acid, brassylic acid, maleicacid, fumaric acid, glutaconic acid, α-hydromuconic acid, β-hydromuconicacid, α-butyl-α-ethyl-glutaric acid, α,β-diethylsuccinic acid,isophthalic acid, terephthalic acid, hemimellitic acid, and1,4-cyclohexanedicarboxylic acid. Any suitable polyhydric alcohol,including both aliphatic and aromatic, may be used such as ethyleneglycol, propylene glycol, trimethylene glycol, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, glycerol,1,1,1-trimethylolpropane, 1,1,1-trimethylolethane, 1,2,6-hexanetriol,α-methyl glucoside, pentaerythritol, and sorbitol. Also included withinthe term "polyhydric alcohols" are compounds derived from phenol such as2,2-bis(4-hydroxylphenyl)propane, commonly known as Bisphenol A.

Any suitable polyoxyalkylene polyether polyol may be used such as thepolymerization product of an alkylene oxide or a mixture of alkyleneoxides with a polyhydric alcohol as an initiator. Examples of alkyleneoxides include ethylene oxide, propylene oxide, butylene oxide, amyleneoxide, mixtures thereof, tetrahydrofuran, alkylene oxide-tetrahydrofuranmixtures, epihalohydrins, and aralkylene oxides such as styrene oxide.Suitable initiators include both aliphatic and aromatics alcohols, suchas ethylene glycol, propylene glycol, dipropylene glycol, trimethyleneglycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol,1,4-pentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol,glycerol, 1,1,1-trimethylolpropane, 1,1,1-trimethylolethane,1,2,6-hexanetriol, α-methyl glucoside, pentaerythritol, sorbitol, and2,2-bis(4-hydroxyphenyl)propane.

The polyoxyalkylene polyether polyols may have either secondary hydroxylgroups or a mixture of primary and secondary hydroxyl groups. If thelatter, the mixture should have a majority of secondary hydroxyl groups.Included among the polyether polyols are polyoxyethylene glycol,polyoxypropylene glycol, polyoxypropylene glycerine, polyoxybutyleneglycol, polytetramethylene glycol, block copolymers, for example,combinations of polyoxypropylene and polyoxyethylene glycols,poly-1,2-oxybutylene and polyoxyethylene glycols, poly-1,4-oxybutyleneand polyoxyethylene glycols, and random copolymer glycols prepared fromblends of two or more alkylene oxides or by the sequential addition oftwo or more alkylene oxides. The polyoxyalkylene polyether polyols maybe prepared by any known process such as, for example, the processdisclosed by Wurtz in 1859, Encyclopedia of Chemical Technology, Vol. 7,pp. 257-262, published by Interscience Publishers, Inc. (1951) or inU.S. Pat. No. 1,922,459.

Polyethers which are preferred as the isocyanate-reactive component (II)include the alkylene oxide addition products of trimethyolpropane,glycerine, propylene glycol, dipropylene glycol, and2,2'-(4,4'-hydroxyphenyl)propane and mixtures of diols and triols suchas propylene glycol-glycerine blends. The most preferred diols andtriols are propylene glycol, glycerine, and mixtures thereof.

Alkylene oxides which are preferred are ethylene oxide and propyleneoxide or mixtures thereof, which are reacted with the above initiatorsto make polyoxyalkylene polyether polyols having predominatelypolyoxypropylene groups with from 0 to 30 percent by weightpolyoxyethylene groups as an end cap, a block, or heteric, preferably asa cap.

The polyether polyols of the invention have a number average molecularweight ranging from 500 to 10,000, preferably from 2000 to 6,000, withaverage functionalities from 1.5 to about 4.0, preferably from 1.8 to3.0. Hydroxyl numbers will generally range from about 11 to 225. Themost preferred polyols will have a number average molecular weight offrom 2000 to 4000.

Particularly suitable polyols are the propylene oxide and ethylene oxideadducts of propylene glycol, glycerine and/or mixtures thereof, withcharacteristics as described above. Most preferably, however, suchpolyols will have a number average molecular weight of 3000 to 6000, afunctionality of 1.8 to 3.0 and a hydroxyl number of 25 to 85.

Polyols containing graft polymer dispersions may also be employed in theinvention as isocyanate-reactive component (II).

Graft polyols are well-known in the art and prepared by the in situpolymerization of one or more vinyl monomers, preferably acrylonitrileand styrene, in the presence of a polyether or polyester polyol,especially polyols containing a minor amount of natural or inducedunsaturation. Methods of preparing such graft polyols may be found incolumns 1-5 and in the examples of U.S. Pat. No. 3,652,639; in columns1-6 in the examples of U.S. Pat. No. 3,823,201; particularly in columns2-8 in the examples of U.S. Pat. Nos. 4,690,956; and 4,524,157, all ofwhich patents are herein incorporated by reference.

In addition to isocyanate prepolymers (I) and isocyanate-reactivecomponent (II), the polyurethane compositions of the invention willlikewise comprise chain-extending agents (III). Chain-extending agents(III) which may be employed include those compounds having at least twofunctional groups bearing active hydrogen atoms such as hydrazine,primary and secondary diamines, amino alcohols, amino acids, hydroxyacids, glycols, or mixtures thereof. Such agents will generally have anumber average molecular weight of less than about 400. A preferredgroup of chain-extending agents includes, water, ethylene glycol,1,4-butanediol, diethylene glycol, and primary and secondary diamineswhich react more readily with the prepolymer than does water such asphenylene diamine, 1,4-cyclohexane-bis-(methylamine), diethyl toluenediamine, ethylenediamine, diethylenetriamine,N-(2-hydroxypropyl)ethylenediamine,N,N'-di(2-hydroxypropyl)ethylenediamine, piperazine, and2-methylpiperazine. 1,4 butane diol, ethylene glycol, diethylene glycoland mixtures thereof are the most preferred chain extending agents(III).

Those skilled in the art will appreciate that some of the compoundsdiscussed above as suitable chain extenders (III) will also be capableof serving, sometimes simultaneously, as catalysts, i.e. as an additive(V).

In addition to the isocyanate prepolymer (I), the isocyanate reactivecomponent (II), and the chain extender (III), the polyurethanecomposition of the invention will also contain a blowing agent (IV)which may be comprised solely or principally of water. While it is mostpreferred that the blowing agent (IV) be comprised solely of water, itis within the scope of the invention that the blowing agent (III) becomprised only principally or primarily of water. As used herein, theterm "principally" shall be defined to mean a blowing agent whereinwater contributes to at least half of the overall blow of the foam.Those skilled in the art will appreciate that the actual amount orpercentage of water used as part of the overall blowing agent (IV) willdepend upon the composition of any co-blowing agent(s). The amount ofwater in a `principally` water blown formulation will be at least 0.04percent of the total blowing agent, while the most preferred amount ofwater in a `principally` water blown formula will be 100% as based onthe total weight of blowing agent.

In the event that the blowing agent is comprised only principally ofwater, the blowing agent (IV) may further be comprised of chemicallyinert low boiling hydrocarbons or halogenated hydrocarbons. Examples ofsuitable halogenated hydrocarbons are those having boiling points below50° C., preferably between -50° C. and 30° C. at atmospheric pressure.Illustrative examples include halogenated hydrocarbons such asmonochlorodifluoromethane, dichloromonofluoromethane,dichlorofluoromethane, and mixtures thereof as well as hydrocarbons sucha propane, n-butane, and isobutane as well as dimethylether, n-pentane,and cyclopentane.

In general, the blowing agent (IV) can consist of between 0.04 to 1.0percent by weight, preferably 0.2 to 0.5 percent by weight of water andfrom 0.5 to 100 percent by weight, preferably 1.0 to 50 percent byweight halogenated hydrocarbons and/or hydrocarbons, with the respectivepercents by weight being based on the total weight of the blowing agent(IV).

In general, depending upon its composition, the blowing agent (IV) willbe present in a amount of from 0.2 to 10.0 percent by weight based onthe weight of the isocyanate-reactive component (II). More preferably,the polyurethane composition of the invention will contain from 0.2 to1.0 percent by weight blowing agent and most preferably from 0.2 to 0.5percent by weight blowing agent based on the weight of theisocyanate-reactive component (II).

In addition to the above, the polyurethane composition may optionallycontain one or more additives (V) selected from the group consisting ofsurface active agents, catalysts, stabilizers, dyes, fillers, pigments,flame inhibitors, antioxidants, plasticizers, and the like, as well asmixtures thereof.

Any suitable catalyst may be used, including tertiary amines such as,for example, triethylenediamine, N-methylmorpholine, N-ethylmorpholine,diethylethanolamine, N-cocomorpholine,1-methyl-4-dimethylaminoethylpiperazine, 3-methoxypropyldimethylamine,N,N,N'-trimethylisopropyl propylenediamine,3-diethylaminopropyldiethylamine, dimethylbenzylamine, and the like.Other suitable catalysts are, for example, stannous chloride, dibutyltindi-2-ethyl hexanoate, stannous oxide, as well as other organometalliccompounds such as are disclosed in U.S. Pat. No. 2,846,408.

A surfactant or surface-active agent may be necessary for the productionof high grade polyurethane foam and articles. Numerous surface-activeagents have been found satisfactory. Nonionic surface-active agents arepreferred. Of these, the nonionic surface-active agents such as thewell-known silicones have been found particularly desirable. Othersurface-active agents which are operative, include paraffin oils, castoroil, turkey red oil, polyethylene glycol ethers of long chain alcohols,tertiary amine or alkanolamine salts of long chain alkyl acid sulfateesters, alkyl sulfonic esters, and alkyl arylsulfonic acids.

Among the flame retardants which may be employed are pentabromodiphenyloxide, dibromopropanol, tris(β-chloropropyl)phosphate,2,2-bis(bromoethyl) 1,3-propanediol, tetrakis(2-chloroethyl)ethylenediphosphate, tris(2,3-dibromopropyl)phosphate,tris(β-chloroethyl)phosphate, tris(1,2-dichloropropyl)phosphate,bis-(2-chloroethyl) 2-chloroethylphosphonate, molybdenum trioxide,ammonium molybdate, ammonium phosphate, pentabromodiphenyloxide,tricresyl phosphate, hexabromocyclododecane, melamine, antimonypentoxide, and dibromoethyl-dibromocyclohexane antimony trioxide. Theconcentrations of flame retardant compounds which may be employed rangefrom 5 to 25 parts per 100 parts of the total resin side.

Preferred pigments and/or dyes include carbon black and dispersions ofthe same in resin and/or solvent.

The isocyanate prepolymer (I) and the resin side, i.e. components (II),(III), (IV) and optionally (V), may be mixed at temperatures from 15° C.to 90° C., preferably at tank temperatures from 20° C. to 35° C., andmay be poured or sprayed into an open mold which is subsequentlyoptionally closed, or may be injected at high pressures into a closedmold. The mixing can be performed mechanically by means of a stirrer orunder high pressure by the impingement method. The mold temperatureshould be from about 20° C. to 60° C., preferably 30° C. to 60° C. Theresultant microcellular polyurethane moldings are primarily intended foruse in the sealing device market but other possible applications includeuse as head rests, spoilers, bumpers and seating applications in theautomotive field as well as nonautomotive uses such as shoe soles.

As indicated at the above, performance properties indicating strength,hardness and compression characteristics are particularly important inthe characterization of sealing devices. It has been found that in orderfor the sealing devices to perform optimally, they must possessparticular values for the physical parameters indicative of strength,hardness and compression characteristics.

In particular, it has been found that molded polyurethane articlesintended for use as sealing devices should possess compression forcedeflection values of less than 15 psi and most preferably between 5 to10 psi at 25 percent deflection when tested per ASTM D3574 Test C.

In addition, it has been found that even after said foam has been agedfor seven days at 158° F. with an allowance of at least 16 but not morethan 96 hours to recover, there should be no more than a plus or minus25 and most preferably 20 percent change from the original deflectionvalues. Such testing is generally done per ASTM D3574 Test K.

With respect to compression set values it has been found that whentested at 158° F., there should be no more than a 20 and most preferably15 percent maximum set average at a 50 percent deflection after thematerial has been aged 22 hours at 158° F. with a 30 minute recovery.See ASTM D3574 Test D.

Similarly, for compression set measured at 180° F., there should be nomore than a 30 percent set average at a 50 percent deflection afteraging 22 hours at 180° F. with a 30 minute recovery. See ASTM D3574 TestD with temperature change only.

In general, the molded polyurethane sealing devices must have a uniformskin and be free of surface irregularities and tears on the mold surfaceside. It should be relatively free of surface pinholes and voids. Inaddition, the polyurethane material must be capable of adhering to metaland/or plastic substrates.

Finally, the polyurethane composition must possess a reactivity profileconsistent with generally accepted processing requirements. Suchreactivity profiles are illustrated below.

The following working examples describe the manner and process of makingand using the invention and set forth the best mode contemplated by theinventors of carrying out the invention, but are not to be construed aslimiting.

The following ingredients were employed to make the isocyanateprepolymer (I) the polyurethane composition of the invention, and themolded microcellular polyurethane articles prepared therewith:

Polyol A is a propylene oxide-ethylene oxide adduct of TMP having amolecular weight of about 5,000; a hydroxyl number of about 25, and aviscosity of about 1400 cPs. It has approximately 15 percent EO.

Polyol B is a propylene oxide-ethylene oxide adduct of glycerine havingapproximately 16 weight percent ethylene oxide and an OH number of 35.

Isocyanate A is a modified MDI containing about 75 weight percent MDI,the remainder being a temperature controlled equilibrium ofuretonimine-containing molecules and carbodimide containing-molecules.

Isocyanate B is essentially pure 98% 4,4'-MDI and 2% 2,4'-MDI. (MS)

DABCO BL-17 is a delayed action catalyst for water/isocyanate reactionin polyurethane foam, commercially available from Air Products andChemicals, Inc.

FOAMREZ UL-29 a polyurethane catalyst believed to be dioctyltindiisooctylmercaptoacetate. It is commercially available from WitcoCorporation.

DABCO DC-1 and DC-2 are proprietary blends of delayed action tin andamine catalysts commercially available from Air Products and ChemicalsCo.

Additive A is a dispersion of carbon black in Dow Polyol, and iscommercially available from Penn Color as EX-678B.

All parts are in parts by weight unless otherwise indicated.

EXAMPLE 1

Isocyanate blend (a) was prepared by charging 1784.55 grams ofisocyanate B and 584.85 grams of isocyanate A to a reactor which hadbeen preheated to a temperature of 50°. The contents of the reactor wereagitated and the reactor temperature adjusted to 50° C. To the resultantisocyanate blend (a) was added 1620.48 grams of polyol A over the courseof about 60 minutes. Subsequently, the reactor contents were heated to60° C. and reacted 60° C. for two hours. The reactor contents weresubsequently cooled to 35° C. and discharged through a 25-micron filterinto a 55 gallon drum container. The net product weighed 500 pounds.

The free NCO-content of the resultant isocyanate prepolymer (I)composition was 18.44 weight percent. The isocyanate prepolymercomposition (I) had a viscosity of 512 cPs at 25° C.

The following examples illustrate polyurethane compositions and moldedpolyurethane articles, produced using the isocyanate prepolymercomposition of Example 1.

EXAMPLE 2

A polyurethane composition intended for use in the production of molded,microcellular polyurethane articles was prepared as follows.

A resin side component (#2) was prepared using the following components:

    ______________________________________                                        Resin Side #2  Weight Percent                                                 ______________________________________                                        Polyol B       87.93                                                          1,4 BDO        8.00                                                           BL-17          0.30                                                           DC-1           0.30                                                           UL-29          0.01                                                           Additive A     3.00                                                           Water          0.46                                                           ______________________________________                                    

Resin side (#2) was combined with the isocyanate prepolymer of Example 1at a 1.03 index.

The polyurethane composition was placed in a low pressure moldingmachine. The resin side of the composition was at a temperature ofbetween 75° to 85° F., while the isocyanate prepolymer was at atemperature of between 75° to 85° F. The mold temperature was between75° to 120° F. After approximately 4-6 minutes the resulting molded foampart was removed from the mold.

The resultant gasket exhibited particularly desirable performanceproperties as indicated below.

    ______________________________________                                        TEST          UNITS   REP.   VALUE AVG. VALUE                                 ______________________________________                                        Orig. peak tensile                                                                          psi     1      92.90 92.97                                                            2      89.50                                                                  3      96.50                                            Orig. break elong.                                                                          (%)     1      120.00                                                                              123.33                                                           2      120.00                                                                 3      130.00                                           Orig/Orig hu 25% CFD                                                                        psi     1      11.667                                                                              11.631                                                           2      11.595                                           ______________________________________                                    

The above numbers illustrate that the values for compression force andtensile strength are desirable.

EXAMPLE 3

A polyurethane composition intended for use in the production of molded,microcellular polyurethane articles was prepared as follows.

A resin side component (#3) was prepared using the following components:

    ______________________________________                                        Resin Side #3  Weight Percent                                                 ______________________________________                                        Polyol B       89.93                                                          EG             5.00                                                           DEG            1.00                                                           BL-17          0.30                                                           DC-1           0.30                                                           UL-29          0.01                                                           Additive A     3.00                                                           Water          0.46                                                           ______________________________________                                    

Resin side (#3) was combined with the isocyanate prepolymer of Example 1at a 1.03 index.

The polyurethane composition was placed in a low pressure moldingmachine. The resin side of the composition was at a temperature ofbetween 75° to 85° F., while the isocyanate prepolymer was at atemperature of between 75° to 85° F. The mold temperature was between75° to 120° F. After approximately 4-6 minutes the resulting molded foampart was removed from the mold.

The resultant gasket exhibited particularly desirable performanceproperties as indicated below.

    ______________________________________                                        TEST          UNITS   REP.   VALUE AVG. VALUE                                 ______________________________________                                        Orig. peak tensile                                                                          psi     1      84.30 84.93                                                            2      87.30                                                                  3      83.20                                            Orig. break elong.                                                                          (%)     1      130.00                                                                              130.00                                                           2      130.00                                                                 3      130.00                                           Orig/Orig hu 25% CFD                                                                        psi     1      10.706                                                                              10.758                                                           2      10.810                                           ______________________________________                                    

EXAMPLE 4

A polyurethane composition intended for use in the production of molded,microcellular polyurethane articles was prepared as follows.

A resin side component (#4) was prepared using the following components:

    ______________________________________                                        Resin Side #4  Weight Percent                                                 ______________________________________                                        Polyol B       88.11                                                          BDO            8.00                                                           BL-17          0.30                                                           DC-1           0.10                                                           DC-2           0.02                                                           UL-29          0.01                                                           Additive A     3.00                                                           Water          0.46                                                           ______________________________________                                    

Resin side (#4) was combined with the isocyanate prepolymer of Example 1at a 1.03 index.

The polyurethane composition was placed in a low pressure moldingmachine. The resin side of the composition was at a temperature ofbetween 75° to 85° F., while the isocyanate prepolymer was at atemperature of between 75° to 85° F. The mold temperature was between75° to 120° F. After approximately 4-6 minutes the resulting molded foampart was removed from the mold.

The resultant gasket exhibited particularly desirable performanceproperties as indicated below.

    ______________________________________                                        TEST          UNITS   REP.   VALUE AVG. VALUE                                 ______________________________________                                        Orig. peak tensile                                                                          psi     1      87.90 84.93                                                            2      85.20                                                                  3      81.70                                            Orig. break elong.                                                                          (%)     1      140.00                                                                              126.67                                                           2      130.00                                                                 3      110.00                                           Orig/Orig hu 25% CFD                                                                        psi     1      11.976                                                                              12.125                                                           2      12.274                                           180° F. Compression set                                                                             10.45 10.45                                      ______________________________________                                    

It should be understood that while the invention, as shown and describedherein, constitutes a preferred embodiment of the invention, it is notintended to illustrate all possible forms thereof. A variety ofcompositions or articles can be created by one of ordinary skill in theart without departing from the spirit and scope of the inventiondisclosed and claimed.

We claim:
 1. A process of molding polyurethane articles, the processcomprising:providing a polyurethane composition comprising:(I) anisocyanate prepolymer composition having a % free NCO of between 16 and20 and a viscosity of from 200 to 600 cPs, the composition comprisingthe result of reacting:(a) an isocyanate blend comprising:(i) 0 to 10pbw 2,4'-diphenylmethane diisocyanate; (ii) 30 to 80 pbw4,4'-diphenylmethane diisocyanate; and (iii) 1 to 10 pbw of a mixture ofuretonimine containing molecules and carbodiimide containing molecules;and (b) from 10 to 70 pbw of an ethoxylated and propoxylated glycerinehaving a number average molecular weight of between 1,000 and 10,000 anda hydroxyl number of between 20 to 100 wherein all pbw are based on thetotal weight of (a) and (b); (II) an isocyanate-reactive component;(III) a chain extender; and (IV) a blowing agent consisting essentiallyof water; and placing the polyurethane composition inside a mold for aperiod of time sufficient to produce a molded polyurethane article. 2.The process of claim 1, wherein the step of providing a polyurethanecomposition comprises providing an isocyanate prepolymer composition (I)wherein the isocyanate blend (a) further comprises:(i) 0-5 pbw2,4'-diphenylmethane diisocyanate; (ii) 40-70 pbw 4,4'-diphenylmethanediisocyanate; (iii) 1-7 pbw of a mixture of uretonimine-containingmolecules and carbodiimide molecules.
 3. The process of claim 1, whereinthe step of providing a polyurethane composition comprises providing anisocyanate prepolymer composition (I) wherein the isocyanate blend (a)further comprises:(i) 0 to 3 pbw 2,4'-diphenylmethane diisocyanate; (ii)45 to 65 pbw 4,4'-diphenylmethane diisocyanate; and (iii) 1 to 5 pbw ofa mixture or uretonimine-containing molecules andcarbodiimide-containing molecules.
 4. The process of claim 1, furthercomprising providing a polyurethane composition comprising an isocyanateprepolymer composition (I) which is a result of reacting an isocyanateblend (a) with from 30-50 pbw of an ethoxylated and propoxylatedglycerin (b).
 5. The process of claim 1, further comprising providing apolyurethane composition comprising an isocyanate prepolymer composition(I) which is a result of reacting an isocyanate blend (a) with anethoxylated and propoxylated glycerin (b) having a number averagemolecular weight of between 4000 to
 6000. 6. The process of claim 1,further comprising providing a polyurethane composition comprising anisocyanate prepolymer composition (I) which is a result of reacting anisocyanate blend (a) with an ethoxylated and propoxylated glycerin (b)having a hydroxyl number of between 20 and
 30. 7. The process of claim1, further comprising providing a polyurethane composition comprising anisocyanate prepolymer composition (I) which is the result of reacting(a)an isocyanate blend comprising(i) 0 to 3 pbw 2,4'-diphenylmethanediisocyanate; (ii) 45 to 65 pbw 4,4'-diphenylmethane diisocyanate; and(iii) 1 to 5 pbw of a mixture of uretonimine containing molecules andcarbodiimide containing molecules; and (b) from 30 to 50 pbw of anethoxylated and propoxylated glycerin having a number average molecularweight of between 4000 and 6000 and a hydroxyl number of between 20 to30.
 8. The process of claim 1, further comprising providing apolyurethane composition wherein isocyanate prepolymer composition (I)has a percent free NCO of from 17 to
 19. 9. The process of claim 1,wherein the resultant molded polyurethane article has a compressionforce deflection value of less than 15 psi.